Also, did you try the capacitive sensor with both ends attached to a foil outside the tank?
I suppose the point is moot since there is already a hole with a bolt in the tank for the KiB system.
The commercial sensors I had on my boat had both leads on the outside.
That does not mean you have to do it that way... any way will work, but it is a more elegant design for tanks that don't already have a hole in them.
The two aluminum tape strips can be as much as 18~24" high, and are the HVAC foil tape. The copper pads attach with adhesive backing to the aluminum tape strips. There is no direct connection from the copper pads to the aluminum - other than capacitive coupling.
I don't remember the exact restrictions to placing the aluminum foil tape. But if I recall there has to be a min/max separation and a min/max length. I am sure I could locate installation instructions.
The connector has VCC, GND, and an analog output.
The two white leads of course are the sensor leads.